We have devised a program to identify and isolate an activated oncogene from a murine tumor. Purified DNA from a murine hepatoma maintained as a transplantable tumor in C3H mice was used to transfect NIH 3T3 cells by the calcium-phosphate coprecipitation method. We were able to obtain transformed foci at high frequencies from this experiment. The cells derived from the foci exhibited all of the properties of transformed cells. To ensure that the transformation is due to the acquisition of foreign DNA, the hepatoma cell DNA was mixed with bacterial plasmid pBR322 DNA and this mixture was used to transform NIH 3T3 cells. The primary transformants contained plasmid DNA sequences indicating DNA transfer. We also have tested the ability of 15 different restriction endonucleases to affect the activity of the gene. Of the enzymes tested, we found three which did not destroy the activity of the gene. DNA from several primary transformants containing plasmid DNA sequences was used to obtain secondary transformants. Several sets of such cell lines are being examined for common plasmid sequences which would indicate their proximity to the oncogene sequences. We plan to construct a genomic library from an appropriate cell line and screen it for plasmid sequences. Positive clones will be tested for the presence of oncogene sequences by DNA transfection.